Mirror assemblies for use on vehicles are subjected to severe operating conditions including both prolonged vibration as well as extremes in temperatures in various climatic regions. Prior mirror assemblies have included mirror cases formed from metallic materials wherein the edges of the case are bent tightly around a glass mirror element retained therewithin. Such assemblies are quite heavy and therefore very difficult to support in the correction viewing position without large, bulky supporting structures secured to the vehicle. Further, since the glass mirror element often does not mate exactly with the metallic case, the mirror element is retained only loosely therewithin causing an irritating rattle under conditions and periods of vibration. Moreover, when the metallic cases are formed such that the glass element is held tightly and securely therewithin to prevent vibration, the significant differences in coefficients of expansion of the glass and metallic materials would cause the glass element to break due to expansion or contraction of either the element or the case itself in extreme temperatures.
Other attempts have been made to solve these problems by forming mirror cases out of plastic materials. One such prior assembly includes a solid plastic case with sides extending tightly against the mirror and then flat over against the front surface of the mirror. Such assemblies were also susceptible to vibration of the mirror element within the case and had the further drawback of either cracking the glass mirror element or allowing it to pop out of the surrounding case when the assembly was subjected to extremely high temperatures such as those encountered in tropical or semitropical regions. Moreover, the solid plastic case added significantly to the weight of the mirror element itself thereby requiring significant supporting structure for attachment to a particular vehicle.
A further problem with prior known mirror cases is the relatively low yield of acceptable assemblies obtained. In prior assemblies with the case adhered to or located tightly against the edge of the mirror element, any irregularity in the mirror element edge was visible. Such imperfect assemblies had to be rejected under applicable standards of quality. Especially with glass mirrors, where chipping or other minor imperfections often occur during production, the prior cases were such that these elements had to be rejected. Rejection rates for some mirror assemblies reached as high as 30 per cent of total production.
Therefore, prior mirror assemblies have suffered from one or more of these problems of vibration and inadequate retention of the mirror element within the case in extreme temperatures, undesirable weight in the mirror assembly as a whole, and/or unsatisfactory rejection rates for mirror assembly production.